On NASA's recommendation, I'm at loss here

> When specifying font height, or accessing graphs to determine the size of a lower-case character, the distinction between “x” height and overall size should be made.

> As a general recommendation, the “x” height of a font used for important flight-deck documentation should not be below 0.10 inch.

> The recommended height-to-width ratio of a font that is viewed in front of the observer is 5:3.

> The vertical spacing between lines should not be smaller than 25–33% of the overall size of the font.

> The horizontal spacing between characters should be 25% of the overall size and not less than one stroke width.